Details

When binding a shortcut key to numeric keypad keys, e.g. KP_0 through KP_9, with the Meta key as a modifier, the action never triggers. Instead the number is typed in the active application as though the Meta key weren't held.

This is because when keygrabber is not present (the one which appears on Ctrl+r 'Run:' in example), the modifiers (CapsLock, NumLock) are ignored. So the string representation of the, lets say, 'KP_2' is seen by Awesome as 'KP_Down' and 'KP_2' keysym != 'KP_Down' keysym, even though they are mapped to the same button. What keysym to use is determinted by the modifiers which are on.

So to make it work you have 2 options by now:
1. When mapping they keys, use the secondary button name ('KP_Down' instead of 'KP_2')
2. Recompile the WM with my attached patch. It will allow you to map KP_0 - KP_9